1. Field of the Invention
The present invention relates to printed circuit boards, and particularly to the structure of a via of a printed circuit board.
2. Description of Related Art
As well known to those skilled in the art, a conventional printed circuit board (PCB) functions to connect various electronic components to each other on the PCB along a predetermined pattern, and is applied to various electronic goods such as home appliances including digital televisions and advanced telecommunication equipment. A conventional PCB comprises a copper plate on which a circuit pattern is formed, and at least an inner layer.
FIG. 3 is an isometric cutaway view of a portion of a conventional PCB 100 defining a via 180 and a plurality of inner layers 160. The via 180 includes an upper cap (annular ring) 120, a conductive hole 190, a plated sidewall 130, a plurality of clearance holes 170, and a lower cap (annular ring) 140. The clearance holes 170 are circular shaped around the plated sidewall 130 in the inner layers of the PCB 100. Two transmission lines 110, 150 respectively coupled to the upper cap 120 and the lower cap 140, and communicate with each other through the via 180.
The capacitance of the via 180 which depends on the area of the clearance holes 170 is one of the most important parameters for PCB designers, because the capacitance of the via 180 may reduce the quality of a signal transmitted through the via 180.
What is needed, therefore, is a printed circuit board which can solve the above problem.